1. Technical Field
This disclosure relates to diagnostic probes and methods of incorporating diagnostic probes for detecting periodontal disease. More particularly, the present disclosure relates to a non-invasive diagnostic probe which emits and analyzes surface acoustic waves to detect and diagnose periodontal disease.
2. Description of Related Art
The instrument and method disclosed herein is directed to the non-invasive detection and measurement of periodontal disease by means of measuring the depth of detachment of a tooth from its supporting tissue or cementum. Since the crown of a tooth comprises enamel and the root of a tooth comprises dentin, the acoustic impedances of these various tooth elements differ.
From the cementoenamel junction (a well defined boundary between the crown and the root) down towards the root, the tooth, under healthy conditions, is attached to supporting tissue by cementum. In the presence of periodontal disease, a portion of the root is detached from the supporting tissue thus forming a gap from the crown and root boundary downwardly into the gum. The depth and width of the gap differs depending on the extent of disease progression.
U.S. Pat. No. 5,100,318, entitled xe2x80x9cULTRASONIC METHOD AND APPARATUS FOR MEASURING THE PERIODONTAL POCKETxe2x80x9d discloses a dental instrument which impinges an acoustic wave onto the gum surface adjacent to the tooth to be interrogated which creates a longitudinal compression wave well known in ultrasound imaging. However, it is not possible to measure a periodontal gap, i.e., periodontal disease, unless the gap between the tooth and the detached adjacent supporting tissue are on the order of more than about 1 wavelength of the aforementioned longitudinal compression wave which, unfortunately, does not allow for early detection of a disease condition. Moreover, the disease must progress to form an appreciable gap before the instrument detects a diseased condition.
For example, in the case of a gap of smaller dimension (1 wavelength of the compression wave), e.g., a simple detachment of the tooth from its support tissue with no appreciable gap or pocket, the aforementioned longitudinal compressional wave would be reflected from the gum to bone surface without wave propagation down the gap to detect a separation of the tooth from the surrounding support tissue. Moreover, the ""318 device has no means of stabilizing the angle of the transmitted ultrasonic wave relative to the boundary between the tooth and the surrounding tissue due to the fact that the angle of incidence is rarely consistent and is typically defined by the random gum configuration of an individual patient which, in the case of the ""318 patent, would cause unwanted reflections and inaccurate readings.
Problems with the ""318 patent are further exacerbated by the near impossibility of perfectly aligning the axis of transmission of the ultrasonic probe head with the axis of the periodontal pocket without prior knowledge of the orientation of the periodontal pocket, i.e., the ledge of the gum is structured such that in most cases positioning the probe for an incident longitudinal wave which is collinear with a periodontal pocket is extremely difficult. If such alignment is not perfect, the reading will be very inaccurate due to reflections. Moreover, since it is known that the angle to produce a surface acoustic wave on the tooth, in the case of the probe head being rested on the gum, is a function of the longitudinal acoustic wave velocity of the gum and the surface acoustic wave velocity of the tooth, the probability that the gum ledge defines exactly the aforementioned angle of incidence with the probe head, in a given patient, is essentially zero. Thus, the use of the ""318 instrument to produce a surface acoustic wave on the surface of the tooth is very difficult due to the sensitivity of the modal conversion to the angle of incidence of the probe head.
U.S. Pat. No. 5,755,571, entitled xe2x80x9cDIFFERENTIAL MEASUREMENT PERIODONTAL STRUCTURES MAPPING SYSTEMxe2x80x9d discloses an instrument which produces a longitudinal acoustic wave pulse which is transmitted down a water filled periodontal pocket wherein the depth is measured by means of the pulse and echo time of flight. This method still requires that the periodontal pocket have a gap between the tooth surface and the detached adjacent supporting structures on the order of the wavelength of the transmitted wave. If the gap is smaller (or if there is simply a detachment of the tooth from the tissue), this instrument is not capable of detecting the periodontal disease condition. Further, the ""571 instrument is overly invasive in that a second probe is mechanically inserted beneath the tissue to establish the position of the cementoenamel junction. This is typically ineffective in the case where the gap between the tooth and adjacent supporting structure is smaller than the width of the second probe. The use of the ""571 mechanical probe is further deleterious for post treatment use since it may impair the healing process by causing injury and detachment of healing tissue.
Thus, there exists a need to develop an instrument and method of detecting the early stages of periodontal disease, e.g., when only slight separation, i.e., a non-appreciable gap, has formed between the tooth surface and the supporting tissue.
The instrument and method disclosed herein includes the generation of a surface acoustic wave pulse (hereinafter referred to as a xe2x80x9cSAW pulsexe2x80x9d) on a crown surface of a tooth which propagates towards the root of the tooth. In the case of a healthy tooth anatomy, the generated SAW pulse will reflect from the cementoenamel junction and crown and root interface with essentially one strong reflection. This is due to the absence of a surface on which the wave can propagate.
In the presence of periodontal disease, the SAW pulse will strike the crown and root interface resulting in a transmission component and a reflection component in proportion with the acoustic impedance mismatch between the enamel and the dentin and the angle of incidence at the interface. The time of flight of the reflection portion is sensed and used as a datum for the measurement of the depth of detachment. The transmission portion continues travelling along the root surface of the tooth until it strikes a point where the tooth is attached to the support tissue where it is then reflected due to the abrupt change in acoustic impedance at the attachment point. This second reflection constitutes a time of flight which is proportional to the depth of tooth detachment of the root since the SAW pulse has a fixed velocity depending on the medium in which it propagates. It is envisioned that due to boundary conditions, the SAW pulse will follow the irregular contour of the tooth as it propagates.
Modal conversion from a longitudinal acoustic wave pulse in the matching layer and compliant coupling medium to a SAW pulse propagating along the surface of the tooth toward the root takes place after refraction across the boundary between the compliant coupling medium and the tooth surface. The critical angle of incidence to convert the longitudinal acoustic wave pulse to a SAW pulse is a function of the longitudinal acoustic wave velocity of the coupling medium in contact with the tooth surface and the SAW pulse velocity on the tooth surface. The calculation of this angle is well known and defined in the literature: [sin(critical angle)=Vi/Vs]xe2x80x94where Vi is the acoustic wave velocity of the incident longitudinal wave in the coupling medium and Vs is the SAW velocity on a tooth surface.
It is also well known that the SAW pulse velocity is a function of material parameters such as the elastic constant and density of particular materials and is described in the literature, e.g., Ristic, Principles of Acoustic Devices, John Wiley and Sons, Inc., 1983, p.95. The SAW velocity is lower in a medium than the longitudinal acoustic wave velocity thus providing the additional benefit of better resolution due to a shorter wavelength at any given frequency, and allowing a lower frequency of operation for the minimum required resolution.
An electronic microcontroller controls the transmission of acoustic pulses by means of a gated oscillator or a pulse generator connected to an amplifier and matching circuit to drive a piezo or other acoustic wave transmitting transducer. When the transmission of the initial acoustic wave pulse is complete, the microcontroller gates the transducer to a receiver which samples the transducer at fixed time increments while storing the samples in progressive memory locations. The microcontroller then computes the depth of tooth detachment from the supporting tissue based on the elapsed time between the detection of the reflected SAW pulses. The elapsed time is directly calculable from the memory location or locations in which the reflection is stored in that each memory location is coincident with a particular elapsed time after the initial acoustic wave pulse transmission.
It is one object of the present disclosure to provide a non-invasive apparatus and method for detecting and accurately measuring periodontal disease at its earliest stages manifested by detachment of the tooth from adjacent supporting tissue without an appreciable gap or space therebetween heretofore not possible with the prior art.
A further object of the invention is to provide a periodontal probe capable of generating a SAW pulse and detecting its reflection on the tooth surface in a direction of propagation collinear with the root and supporting tissue to reproduceably and accurately measure a periodontal disease condition absent the presence of an appreciable gap or pocket between the tooth and its supporting tissue.
A further object of the invention is to provide a probe capable of ultrasonically measuring periodontal detachment by angularly manipulating the probe head with the tooth surface such that a modal conversion from a longitudinal acoustic wave pulse to a SAW pulse takes place at the interface between the probe head and the tooth surface.
Another object of the present disclosure is to provide an ultrasonic probe which includes a monitor for displaying the depth of detachment of a tooth surface from the supporting tissue and a device for recording the depth measurements with correlation to a particular tooth.